1. Field of the Invention
This invention relates to an integrated and continuous process for producing gaseous and liquid products from coal wherein hydrogen is reacted with coal in a fluid bed hydrocarbonization zone to form char, gaseous and liquid products and wherein the char formed is fed to a fluid-bed gasification zone to generate all the hydrogen-rich gas required for the reaction with coal in the hydrocarbonization zone.
2. Description of the Prior Art
Increasing energy needs have focused attention on solid fossil fuels due to their availability in the United States in a relatively abundant supply and their potential value if converted into more useful forms of energy and feed-stock. Various processes have been developed in an effort to economically and efficiently convert coal to useful products.
In carbonization processes, coal has been coked in an inert atmosphere to produce about 10 to 15 weight percent, based in the coal charged, of a liquid product and about 70 to 75 weight percent of a solid char. The low yield and poor quality of these products rendered them commerically unattractive. The worth of the unit heating value of the solid char product, even with all the gas and liquid product, was less than that of the coal charged.
Hydrogenation processes have been employed to convert the bulk of the coal to a liquid product. In these processes, a recyclable pasting oil has been used to initially dissolve or slurry the raw coal; the slurry of coal and usually a catalyst in oil has been heated in the presence of hydrogen gas at 450.degree. C to 550.degree. C and about 2000 to 10,000 psig.; and up to 20 to 30 percent of the finely-divided unreacted coal and ash had to be filtered off or otherwise removed from the heavy, viscous primary oil product. Although these processes have been successful in that the amount of liquid products substantially increased, they were not commercially acceptable because the investment, the operating costs and in particular, the hydrogen requirements, were too high in comparison with the value of the products obtained. They are considered only in special economic conditions where alternate energy sources such as crude oil are expensive or unavailable. Other processes have been directed toward total gasification. However, total gasification requires large consumption of hydrogen as well as difficult and costly operating conditions.
Hydrocarbonization processes wherein coal has been carbonized in the presence of hydrogen have been employed to obtain gaseous and liquid products. However, these processes generally have been batch-type processes and not convertible to operable continuous processes in any obvious manner. It is shown in U.S. Pat. No. 3,231,486 that a sub-bituminous coal, Elkol coal, may be carbonized under mild operating conditions in the presence of hydrogen in a fluid-bed. And in U.S. Pat. No. 2,634,286, it is taught that char particles formed in a dry hydrogenation zone, which zone is maintained under a pressure of from 250 to 1500 lbs. per sq. in., may be employed to produce a high grade synthesis gas when passed directly to a gasification zone maintained under a pressure of from about 300 to 600 lbs. per sq. in. However, an effective, economical and continuous method of producing gaseous and liquid fuel products from coal remains an important national objective.